Actors

Actors are those entities that represent a person or thing that must interact with the system. An actor is outside the system and can input or receive information. Examination of the requirements and asking a lot of who questions should reveal the actors. The following types of questions can help to identify the actors:

• Who will maintain the system?
• Who will interact with the system?
• Who will use information provided by the system?
• Who will supply information to the system?
• Where will the system be used?
• Are there any external resources?
• What are the roles?

Determining the actors is as much art as science. The best approach is to start with the primary or significant actors. You might consider these as the obvious candidates. Look at the actors and determine their roles and responsibilities. Looking at our problem statement we can determine two immediate candidates: clerk and customer. Should these be the same actor? The question to ask is do they have the same role or different roles? The clerk is to maintain the video rental system. Could a clerk rent videos? Can a customer maintain videos? We could make an argument that it should be one actor, but it probably makes most sense to separate the two. They each have different roles with regard to the system. Another question that could be asked is what external resources are needed? One resource that might be looked at is the video rental library or cataloging system. The problem is that this is not a good actor because it is an intrinsic part of the system. If the rental library were external then it could be considered.

In UML, actors are represented as a stick figure.

Looking at our problem statement provides the following roles to requirements:

• Clerks maintain video information
• Customers rent and return videos

Based on analysis, the following actors can be identified:

• Clerk A person who is authorized to maintain the video library
• Customer A person who is eligible to rent videos